Gearbox for motor vehicles

ABSTRACT

A range gearbox with planetary gear ( 1 ) for motor vehicles intended to be connected to the output side of a basic gearbox. The ring gear ( 18 ) of the planetary gear is axially displaceable. The ring gear ( 18 ) can engage coupling rings ( 10, 16 ) alternatively. A synchronizing means or member ( 15 ) is intended to synchronize the rotational speed difference between the ring gear ( 18 ) and one or other coupling ring ( 10, 16 ). The synchronizing means ( 15 ) and the coupling ring ( 16 ) are arranged coaxially outside the ring gear ( 18 ). A second means or engagement member ( 25 ) for engaging the coupling ring ( 16 ) and a third means or engagement member ( 25, 25   b ) for driving said synchronizing means ( 15 ) are arranged on the external side, as seen radially, of the ring gear ( 18 ). The coupling ring ( 16 ) is arranged between the synchronizing means ( 15 ) and the first means ( 27 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation patent application ofInternational Application No. PCT/SE02/02219 filed 3 Dec. 2002 which waspublished in English pursuant to Article 21(2) of the Patent CooperationTreaty, and which claims priority to Swedish Application No. 0200152-7filed 17 Jan. 2002. Both applications are expressly incorporated hereinby reference in their entireties.

TECHNICAL FIELD

[0002] The present invention relates to a gearbox for motor vehicles,which is arranged between a basic gearbox and a transmission leading todriving wheels. The arrangement comprises (includes, but is not limitedto) an input shaft extending from the basic gearbox, an output shaft tothe transmission, a planetary gear arranged between the input shaft andthe output shaft, the ring gear of which planetary gear can be displacedaxially by a first means capable of instituting axial displacement ofthe ring gear. A first coupling ring is also included for engaging ahigh-range mode, and a second coupling ring is provided for engaging alow-range mode, and coupling rings and the ring gear can engagealternatively. There is at least one synchronizing means having at leastone friction surface, and the synchronizing means is configured tosynchronize the rotational speed difference between the ring gear andone or other coupling ring by interaction with a corresponding, at leastone friction surface that is arranged on each coupling ring. The gearboxis intended to be capable of shifting between two gearings and thus,together with the basic gearbox, doubling the total number of gearingpossibilities.

BACKGROUND ART

[0003] In transmission systems for heavy-duty vehicles, for exampletrucks and buses, it is known to connect an extra gearbox to the basicgearbox of the vehicle for the purpose of doubling the number of gearingpossibilities (see, for example, SE 453379—the equivalent of which isU.S. Pat. No. 4,821,591 and WO 9620359; both U.S. Pat. No. 4,821,591 andWO 9620359 are published in English and are hereby expresslyincorporated herein by reference for purposes of disclosure). Such agearbox is usually referred to as a range gearbox or an auxiliarygearbox. The range gearbox usually comprises a planetary gear, by meansof which the gearing can be changed between a high-range mode and alow-range mode. In the low-range mode, use is made of the gearing in theplanetary gear, whereas, in the high-range mode, no transmission takesplace through the planetary gear. In order to facilitate shiftingbetween high-range mode and low-range mode, it is known to design suchplanetary gears with synchronizing means, usually comprisingsynchronizing rings, spring means for pre-synchronizing and blockingmeans in order to prevent engagement before synchronous rotational speedhas been achieved.

[0004] In order to reduce the number of component parts, and also fromthe point of view of power distribution, it has been found to beadvantageous to use the ring gear of the planetary gear as a couplingsleeve. The ring gear can, by axial displacement and aftersynchronization of the rotational speed difference between the ring gearand coupling rings, be brought into engagement with coupling ringslocated on either side of the planetary gear, and, in this way,different gearings are obtained. Examples of known art with an axiallydisplaceable ring gear are shown in SE514231—the equivalent of which isUS 23110876A1 publication and which is hereby expressly incorporatedherein by reference for purposes of disclosure. In this case, the ringgear is provided at each axial end with synchronizing means, and theinternal teeth of the ring gear are extended so as to be capable ofbeing coupled together with a corresponding coupling ring with couplingteeth arranged on each side of the ring gear. The ring gear and thesynchronizing means on each side thus occupy more space in the axialdirection.

[0005] When the ring gear in SE 514231 (US 23110876A1) is coupledtogether with the gearbox casing, low-range mode is obtained, and thegearing in the planetary gear is used.

[0006] In order to obtain a shorter shifting time when synchronizing therotational speed for the low-range mode, a greater synchronizing torqueis required compared with synchronization for the high-range mode. Alarge diameter of the low-range synchronizing device is thus desirablein order to obtain a greater synchronizing torque. The diameter refersto the position of the synchronizing friction surfaces. In the rangegearbox according to SE 514231 (US 23110876A1), the inside diameter ofthe ring gear limits the possibility of a large synchronizing diameterand thus a great synchronizing torque. Another disadvantage of known artis that the overall length is in many cases too great and that doublesets of annular springs with associated synchronizing rings arerequired.

[0007] An object of the present invention is to make synchronization forthe low-range mode act on as large a diameter as possible in order toobtain more rapid shifts and also to shorten the overall length of thegearbox and reduce the number of component annular springs andsynchronizing rings, while retaining good function. An object is also,when the axial displacement of the ring gear takes place, to separatefriction surfaces in the synchronizing device with a relative speeddifference; that is to say the synchronizing device which is notfunctioning at the time, and in this way reduce the friction losses.

DISCLOSURE OF INVENTION

[0008] Arrangements configured according to the present inventioncomprise a gearbox for motor vehicles that is intended to be connectedto the output side of a basic gearbox and have an input shaft from thebasic gearbox, an output shaft to a transmission, and a planetary geararranged between the input shaft and the output shaft. A ring gear isprovided, and relative to which the planetary gear can be axiallydisplaced by a first means for axial displacement of the ring gear. Thearrangement also comprises a first coupling ring, for engaging ahigh-range mode, and a second coupling ring, for engaging a low-rangemode, with which coupling rings the ring gear can engage alternatively,at least one synchronizing means with at least one friction surface,which synchronizing means is intended to synchronize the rotationalspeed difference between the ring gear and one or other coupling ring byinteraction with a corresponding at least one friction surface arrangedon each coupling ring. The synchronizing means and the second couplingring are arranged coaxially outside the ring gear. A second means forengaging the second coupling ring and a third means for driving saidsynchronizing means are arranged on the external side (as seen radially)of the ring gear, and the second coupling ring is arranged between thesynchronizing means and the first means.

[0009] Major advantages of arrangements configured according to thepresent invention exemplarily include, among others, the shifting time,in particular when shifting to a low-range gear, is shortenedconsiderably. The shorter shifting time is achieved on account of thegreater synchronizing torque which is obtained by virtue of theinvention making it possible to arrange the friction surfaces of thesynchronizing ring along a larger diameter, seen from the centerline ofthe input and output shafts; that is to say, the synchronizing ring islocated coaxially outside the ring gear. Moreover, the overall length ofthe range gearbox is shortened further, and only one annular spring andan associated synchronizing ring, that is to say a double synchronizingring with two friction surfaces, are required.

[0010] According to an advantageous first embodiment of the inventivearrangement, the ring gear has on its external side, as seen radially,bars for engaging the first coupling ring. The advantages are shortoverall length, large synchronizing diameter and simple constructionwith few components.

[0011] According to an advantageous second embodiment of the arrangementaccording to the invention, the internal teeth, as seen radially, of thering gear are used for engaging the first coupling ring. The advantagesof this embodiment are that the external bars of the ring gear can beshortened somewhat and also that manufacture of the first coupling ringis made easier.

[0012] In a further advantageous third embodiment of the arrangementconfigured according to the present invention, the internal teeth of thering gear are helical teeth. The advantage of this is that aservo-effect is obtained when the gear concerned is engaged. The helicalteeth, moreover, provide quieter operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present invention will be described in greater detail belowwith reference to the accompanying drawings which, for the purpose ofexemplification, show further preferred embodiments of the invention, aswell as demonstrate aspects of the invention's technical background. Inthe drawings:

[0014]FIG. 1 is a cross-sectional view showing a longitudinal sectionthrough a range gearbox that is configured according to an embodiment ofthe present invention and that has a high-range mode (direct gear)engaged;

[0015]FIG. 2 is a detailed cross-sectional view showing an enlargementof part of the arrangement of FIG. 1;

[0016]FIG. 3 is a detailed cross-sectional view showing an enlargementof part of the arrangement according to FIG. 1, but with the low-rangemode engaged;

[0017]FIG. 4 is an enlarged cross-sectional view of part of thearrangement according to FIG. 1, but in the phase of synchronization forlow-range mode; and

[0018]FIG. 5 is a diagrammatic view of external bars, blocking teeth andrespective sets of coupling teeth.

MODE FOR THE INVENTION

[0019]FIG. 1 shows a gearbox 1 configured according to the teachings ofthe present invention which advantageously constitute a range gearbox 1intended to be connected to the output shaft of a basic gearbox (notshown) in a heavy-duty vehicle, for example a truck or bus. The rangegearbox comprises a planetary gear 4.

[0020] The output shaft of the basic gearbox forms the input shaft 2 ofthe range gearbox 1. The planetary gear 4 is arranged between the inputshaft 2 of the range gearbox and an output shaft 3 from the rangegearbox. The output shaft forms part of a transmission (not shown) whichtransmits driving power to the driving wheels of the vehicle. Thedriving power is therefore supplied from the engine of the vehicle, viathe basic gearbox, the range gearbox and also via a transmission (notshown), to the driving wheels. A sun gear 5, forming part of theplanetary gear 4, with external teeth 6 is mounted in a rotationallyfixed manner on the input shaft. In the illustrative embodiment shown,the sun gear is integrated in the shaft 2. Alternatively, the sun gearcan be attached to the shaft by means of splines. The sun gear is inengagement with a number of surrounding planet wheels 7 which are eachmounted on their own pivot 8 in a planet-wheel carrier 9 which is inturn connected in a rotationally fixed manner to the output shaft 3. Inthe embodiment shown, the sun gear is also in rotationally fixedengagement with a first coupling ring 10 by means of internal teeth 11on the coupling ring. The coupling ring 10 is arranged in a fixed mannerrelative to the sun gear in the axial direction and is provided withinternal coupling teeth 12. Arranged on the coupling ring 10 is aninward-facing conical friction surface 13, the purpose of which is tointeract with a corresponding outward-facing conical friction surface 14on a synchronizing ring 15.

[0021] A second coupling ring 16 is arranged in a rotationally fixedmanner, as well as in an axially fixed manner relative to a gearboxcasing 17 by means of, for example, external splines (not shown)arranged on the coupling ring 16, together with corresponding internalsplines in the gearbox casing. Arranged on the coupling ring 16 is aninward-facing conical friction surface 23, the purpose of which is tointeract with a corresponding outward-facing conical friction surface 22on the synchronizing ring 15. In the illustrated embodiments, thesynchronizing ring is a double synchronizing ring as it comprises doublefriction surfaces 14 and 22.

[0022] The planet wheels 7 are also in engagement with the internalteeth 19 of a ring gear 18. The ring gear 18 has on its external side,seen radially, a first circumferential groove 20 intended to receive anannular spring 21, the function of which spring is to transmit thepressing force from the ring gear to the synchronizing ring 15 whensynchronization and shifting take place.

[0023] Arranged on the external side, seen radially, of thesynchronizing ring 15, are conical friction surfaces 14 and 22 which,when synchronization takes place, interact respectively with thecorresponding conical friction surfaces 13 and 23 of each coupling ring.Arranged on the internal side of the synchronizing ring 15, as seenradially, are bars 24 which extend in the axial direction. The bars 24are in engagement with corresponding external bars 25 b on the ring gear18. The bars 25 b ensure that the synchronizing ring rotates with thering gear 18, that is to say driving takes place. However, thesynchronizing ring 15 is at the same time limitedly rotatable relativeto the ring gear 18. This is shown by FIG. 5, where the external bar 25b of the ring gear 18 allows only a certain rotation of thesynchronizing ring 15 by virtue of the fact that the bars 24 stopagainst the bar 25 b. A suitable number of bars 25 b along thecircumference of the ring gear is six or nine. Other numbers are alsopossible.

[0024] The ring gear 18 is used as a coupling sleeve and is thus axiallydisplaceable between a high-range mode and a low-range mode. This meansthat the ring gear 18 is axially displaceable relative to thesynchronizing ring 15, the planet wheels 7 and the coupling rings 10 and16. The synchronizing ring 15 is also axially displaceable relative tothe coupling rings 10 and 16.

[0025]FIG. 1 shows a range gear with the high-range gear engaged; thatis to say, the ring gear 18 is engaged so as to rotate with the inputshaft 2. When the driver selects the low-range gear by means of a rangeselector (not shown), an axial force is transmitted in a known manner tothe ring gear 18 and which makes it move to the right in FIG. 1. Thedisplacement of the ring gear 18 takes place via means for displacementof the ring gear. In the illustrative embodiment shown, the meansconsists of a rod 26 which is coupled to the range selector and is inturn connected firmly to a fork 27. The fork is connected rotatably tothe ring gear 18, but is fixed in the axial direction relative to thering gear 18.

[0026] The ring gear is first disengaged from the coupling teeth 12 ofthe coupling ring 10. The annular spring 21 accompanies the ring gear inits movement to the right in FIG. 1. The annular spring 21 is in itscompressed state, that is to say loaded on the bars 24 of thesynchronizing ring 15. The dimensions of the first circumferentialgroove 20 are determined by the dimensions of the annular spring 21 sothat it has space when it is in its compressed state. When the ring gear18 moves to the right, it takes the synchronizing ring 15 with it byvirtue of the straining of the annular spring against the internal bars24 of the synchronizing ring.

[0027] When the ring gear 18 and the synchronizing ring 15 have movedsufficiently far to the right that the conical friction surface 22 comesinto contact with the corresponding conical surface 23 on the couplingring 16, the annular spring 21 is inserted into the groove 30 of thesynchronizing ring 15, and synchronization of the speed differencebetween the ring gear 18 and the coupling ring 16 begins. The speed ofthe coupling ring 16 is zero as it is connected firmly to the gearboxcasing 17. On account of the speed difference between the ring gear andthe coupling ring, the braking torque, that is to say the synchronizingtorque, will rotate the synchronizing ring relative to the ring gear asmuch as the spacing between the two bars 24 with blocking surfaces 28and 29 allows (see FIG. 5). The magnitude of the synchronizing torque isdetermined by, inter alia, the diameter on which the friction surfaces13, 14, 22 and 23 are located. A larger diameter provides a greatersynchronizing torque for a given axial force from the ring gear 18.

[0028] Blocking surfaces 28 and 29 are arranged on the synchronizingring 15. In a known manner the limited rotation of the synchronizingring 15 relative to the ring gear 18 and the blocking surfaces 28, 29 onthe synchronizing ring 15 ensure that the ring gear 18 is blockedagainst further axial movement before synchronous speed has beenachieved. This is effected by one of the blocking surfaces 28 or 29,depending on the direction in which the ring gear 18 is to be displaced.FIG. 5 shows a situation just when synchronous speed has been achievedand the bars 25 of the ring gear enter the next step of being coupledtogether with the coupling teeth 31 on the coupling ring 16. When theblocking surfaces 28, 29 block further displacement, the ring gear 18and the annular spring 21 have been displaced relative to thesynchronizing ring 15 into a position which is shown in FIG. 4. Here,the annular spring 21 has taken up an expanded position in a secondcircumferential groove 30 arranged in the synchronizing ring 15.

[0029] During continued displacement of the ring gear 18, the annularspring 21 is compressed by interaction between the angled edge surfacesof the second circumferential groove 30 and the annular spring 21 and isfinally displaced into a position part way up over the bars 24 (see FIG.3). In this position, the synchronization work has been completed (seealso FIG. 5) and the ring gear 18 can be brought into engagement withthe coupling teeth 31 of the coupling ring 16 in order to lock the ringgear 18 in relation to the gearbox casing 17.

[0030] A corresponding procedure takes place when the ring gear 18 movesfrom low-range mode to high-range mode; that is to say, is displaced tothe left in any of FIGS. 1 to 4.

[0031] The axial surfaces of the second groove 30 have an inclined angleadapted in order that the annular spring 21 will provide a certainpre-synchronizing force when axial movement of the ring gear 18 takesplace. The annular spring can also have a corresponding angled edgesurface. The inclination of the edge surfaces is adapted according to apreviously known method to the synchronizing arrangement concerned so asto achieve optimum synchronization. It is also possible for the annularspring to be received by the second groove instead of the first. Thefirst groove will then be provided with angled edge surfaces in acorresponding way, and the annular spring will jump in and out of thefirst groove instead in a corresponding way.

[0032] The internal teeth 19 of the ring gear can be helical teeth,which can provide a servo effect when the gear concerned is selected;that is to say, the moment of inertia in the gearbox helps to push thering gear 18 in the axial direction. The external and internal bars onthe ring gear and, respectively, the synchronizing ring and also thecoupling teeth of the coupling rings can also be inclined in relation tothe axial center line 32 of the ring gear. This means that when therange gear is engaged (low-range or high-range), balancing of the axialforces takes place. Balancing of the axial forces affords the advantagethat the ring gear does not tend to move in the axial direction, and thefork 27 is thus not subjected to unnecessary stresses. The helical teethmoreover provide quieter operation.

[0033] The external bars on the ring gear and also the positioning ofthe double synchronizing ring coaxially outside the ring gear contributeto the extremely short overall length of the gearbox casing, and agreater synchronizing torque is obtained without the external shiftingforce, which is supplied via the rod 26 and the fork 27, having to beincreased.

[0034] The invention is not limited to the gear arrangement describedabove. It is possible to use other types of resilient elements insteadof an annular spring. The double synchronizing ring can be divided intotwo separate synchronizing rings each with its own cone-shaped frictionsurface and its own second circumferential groove for receiving its ownannular spring. In this embodiment, the ring gear will therefore havetwo first grooves. The grooves in each synchronizing ring ensure thatthe friction surfaces will not be in contact with one another for thesynchronizing ring and coupling ring which are not functioning at thetime. In this way, there are no friction losses or unnecessary wear.

[0035] The double synchronizing ring, which is made in one piece in theillustrative embodiments shown, can be made from several assembledpieces.

[0036] In the illustrative embodiments shown, the friction surfaces inthe coupling rings consist of sheet-metal cones which are, by means offingers, arranged firmly in corresponding holes in the respectivecoupling ring. Alternatively the coupling rings can be made withintegrated cones, which leads to a reduction in the number of componentparts.

[0037] Alternatively, the coupling ring 10 can be connected firmly tothe planet-wheel carrier 9 instead of the sun gear 5.

[0038] Furthermore, the coupling ring 10 can be made with externalcoupling teeth, as seen radially, which then instead engage the internalteeth 19 of the ring gear. In this embodiment, however, the conicalfriction surface 13 is arranged on the coupling ring in the same way asin the illustrative embodiments shown previously.

1. A gearbox (1) for motor vehicles, intended to be connected to theoutput side of a basic gearbox and comprising an input shaft (2) fromthe basic gearbox, an output shaft (3) to a transmission, a planetarygear (4) arranged between the input shaft (2) and the output shaft (3),a ring gear (18) of the planetary gear is axially displaceable by afirst member (27), a first coupling ring (10) that engages a high-rangemode, and a second coupling ring (16) that engages a low-range mode, thecoupling rings (10, 16) and the ring gear (18) alternatively engage atleast one synchronizing member (15) with at least one friction surface(14, 22), which synchronizing member (15) is configured to synchronizethe rotational speed difference between the ring gear (18) and one ofthe coupling rings (10, 16) by interaction with a corresponding frictionsurface (13, 23) arranged on each coupling ring (10, 16), thesynchronizing member (15) and the second coupling ring (16) arecoaxially arranged outside the ring gear (18), a second engagementmember (25) configured to engage at least the second coupling ring (16)and a third engagement member (25, 25 b) configured to drive saidsynchronizing member (15) are arranged on a radially external side ofthe ring gear (18), and the second coupling ring (16) is arrangedbetween the synchronizing member (15) and the first member (27).
 2. Thegearbox as recited in claim 1, wherein the second engagement member (25)is engageable with the first coupling ring (10).
 3. The gearbox asrecited in claim 1, wherein at least one internal bar is radiallyarranged on an internal side of the ring gear (18) and correspondingcoupling teeth on the first coupling ring (10) are arranged on aradially external side of the first coupling ring (10).
 4. The gearboxas recited in claim 3, wherein said internal bars in the ring gear (18)constitute some of the internal teeth (19) of the ring gear (18) andwhich interact with planet wheels (7) forming part of the planetarygear.
 5. The gearbox as recited in claim 1, wherein the secondengagement member (25) and the third engagement member (25, 25 b)constitute a combined fourth member (25, 25 b) that drives saidsynchronizing member (15) and engages at least one of the coupling rings(10,16).
 6. The gearbox as recited in claim 5, wherein bars (25, 25 b)constitute at least one of: the second means (25), and the third means(25, 25 b) and the fourth means (25, 25 b).
 7. The gearbox as recited inclaim 1, wherein at least one synchronizing ring (15) constitutes thesynchronizing member (15).
 8. The gearbox as recited in claim 7, whereinthe synchronizing rings (15) are assembled into a double synchronizingring (15) engageable with the two coupling rings (10, 16).
 9. Thegearbox as recited in claim 1, wherein the ring gear (18) has at leastone first circumferential groove (20) on a radially external sidethereof.
 10. The gearbox as recited in claim 9, wherein the ring gear(18) has at least one second circumferential groove (30) on the radiallyexternal side thereof.
 11. The gearbox as recited in claim 10, whereinan essentially annular, radially resilient element (21) is arranged inat least on of the first (20) and second (30) grooves and which ismoveable into and out of the respective groove (20, 30) when the ringgear (18) is displaced axially relative to the synchronizing member(15).
 12. The gearbox as recited in claim 11, wherein the element (21)is an annular spring (21) which has an interruption in itscircumferential direction.
 13. The gearbox as recited in claim 1,wherein blocking surfaces (28, 29) are arranged on the synchronizingmember (15) and configured to block engagement of said coupling rings(10, 16) and the ring gear (18) before synchronous rotational speed isachieved.
 14. The gearbox as recited in claim 1, wherein internal teeth(19) of the ring gear (18) are angled in a tangential plane in relationto the axial centerline (32) of the ring gear (18) and is configured tobring about a servo effect upon axial movement of the ring gear (18),and in that said angling induces counterclockwise displacement withincreasing distance from one shaft end of the gearwheel (18).
 15. Thegearbox as recited in claim 14, wherein said bars (25) arranged on theexternal side of the ring gear (18) and coupling teeth (31) alsoarranged on the coupling ring (16) are angled in the tangential plane inrelation to the axial centerline (32) of the ring gear (18) and areconfigured to balance axial force acting on the ring gear when theinternal teeth of the ring gear are angled.